ABSTRACT: The laboratory rat Rattus norvegicus utilizes a variety of sensory cues to orient in the dark, most notably vision, hearing, olfaction and spatial memory. It has been suggested that rats also echolocate, but the evidence is scanty and contradictory. On the basis of pilot studies, I propose to use systematic impairment experiments to determine whether rats echolocate. Success in avoiding a barrier will be compared (1) to blind and deaf-blind animals, (2) in blind and blind-mute animals, and (3) in a noisy and a quiet environment. Ultrasonic vocalizations will be monitored throughout. The results will determine whether acoustic detection of distant objects is possible and whether this is done by an active echolocation system utilizing vocal cries or passively using room noises.